UPDATE: The paragraph also has to be over a certain amount of text in order to break the buttons from displaying in their collapsed state! Also this only seems to be an issue with the sidebar assigned on the left not on the right!
The problem lies in that you’ve enabled the Shadow feature for the Button stack. It may seem innocuous, but shadows can be a bit of a problem in Stacks. Stacks wraps everthing own the page in multiple <div> tags and then applies overflow: hidden to each of them. This overflow attribute prevents shadows from being shown outside of their own stack. To combat this developers have to use code to disable the overflow attribute on the element and its parents elements so the shadow can be seen.
You use of it inside the sidebar is turning off the sidebar’s needed overflow attribute, and the content is becoming visible.
Now you’ll say – But I have “Disable at Mobile Breakpoint” checked. Shouldn’t that fix it? Unfortunately that can only hide the shadow. The javascript that applies overflow: visible to the stack and its parent stacks is still active.
Why this isn’t happening with the right-hand placed side bar I’m not sure. I’ll have to dig a bit to find out. But considering it is Saturday and I’ve not even had a cup of coffee yet, that is going to have to wait.
TL;DR – For now, turn off the button shadows and you should be A-OK. I’ll look and see if there’s not something I can do to allow the shadows in the sidebar though. I do think it should be possible.
